The fabrication of a semiconductor device conventionally uses a sputtering system to form a metal layer on a substrate. A silicon wafer is positioned in opposition to a target of a required film forming material in a processing vessel. The sputtering processing vessel has an inlet and an outlet. Processing gas is introduced into the vessel from the inlet and a vacuum pump is connected with the outlet to attract the processing gas in the vessel. The interior of the processing vessel is maintained at a required low-pressure atmosphere, whereby particles sputtered from the target are applied to the objects.
The metal target is placed on a target holder and the silicon wafer is on a substrate holder. Direct-current power supply is applied to the target holder and the substrate holder, and the processing gas is ionized to form plasma between the target and the silicon wafer. In order to allow the positive ions of the plasma to collide with the surface of the target, the cathode of a power supply is connected to the target holder.
With recent developments in high-density integration of semiconductor devices, techniques for filling in submicron vias must be developed. However, known sputtering processes exhibit low step coverage characteristics. As contact holes of integrated circuits have a large aspect ratio, wiring discontinuities tend to occur at the bottom of the holes. In high-integration integrated circuit, the problem of incomplete-filling of the contact holes often occurs.
A sputtering processing apparatus with a collimator is used to enhance the step coverage of sputtering processes. By using the collimator, the metal sputtering process may be applied to the fabrication of 0.35-micron integrated circuits, even that of 0.25-micron integrated circuits.
Referring to FIG. 1, a schematic cross sectional view of a sputtering processing vessel 100 is shown. A target holder 145 is at the upper inner portion of the sputtering processing vessel 100 and a target 150 is attached to the bottom surface of the target holder. In general, the direct-current sputtering process is used for a deposition of metal or barrier material and the target 150 consists of that material.
A substrate holder 140 is placed at the lower inner portion of the sputtering processing vessel 100 and a silicon wafer 160 is placed on the top surface of the substrate holder. During the sputtering process, ionized gas collides with the bottom surface of the target 150 and metal ions are deposited on the top surface of the silicon wafer 160. Thus, the target 150 must be connected to the cathode of a direct-current power supply and the substrate holder 140 for supporting the silicon wafer 160 should be connected to the anode of the direct-current power supply or to ground.
The sputtering processing vessel 100 has an inlet 109 and an outlet 110. Processing gas for the sputtering process is introduced into the sputtering processing vessel 100 from the inlet 109. A vacuum pump connects with the outlet 100 for attracting the processing gas in the sputtering processing vessel 100. The processing gas typically comprises argon (Ar) and nitrogen (N.sub.2).
The metal atoms, which are bombarded by ionized gas, leave the surface of the target 150 at a large angle and a small angle, with respect to the direction perpendicular to the surface of the target 150. The metal atoms cannot be perpendicularly deposited on the silicon wafer 160 and the step coverage for the contact holes in the silicon wafer 160 is poor. By using the metal sputtering process, incomplete fillings often form in high aspect-ratio contact holes and the contact resistance of the contact hole will significantly increase.
A collimator 170 is placed between the silicon wafer 160 and the target 150, as demonstrated in FIG. 2, to improve the step coverage of the sputtering process. A pair of supporters 165 are positioned on the inner surface of the sputtering processing vessel 100 between the target 150 and the silicon wafer 160. The supporters 165 protrude from the surface of the sputtering processing vessel 100 to form two protrusions. The supporters 165 are opposed to each other and the collimator 170 is placed on the pair of supporters. Referring to FIG. 3, a top view of the portion of the collimator 170 according to FIG. 2 is demonstrated. The collimator 170 consists of a plurality of through-holes 10.
The step coverage of the sputtering process is improved by using the sputtering apparatus with the collimator 170. As target atoms leave the surface of the target 150 at a large inclined angle with respect to a direction perpendicular to the surface of the target 150, these atoms will contact the sidewalls of the through-holes 10 and not contact the silicon wafer 160. Consequently, only the small-angle target atoms contact the surface of the silicon wafer 160 and the step coverage of the contact holes is enhanced.
The function of the collimator 170 depends on the geometry-design. In general, the aspect ratio of the through-hole 10 is about 1:1 or 1.5:1. A step-coverage ability of a sputtering process by using a collimator with an aspect-ratio about 2:1 is enhanced by 10% to 25% as compared to a conventional sputtering process.
The silicon wafer 160 must be heated during the sputtering process an the collimator 170 is also heated. The collimator 170 consists of plural through-holes 10 and it is made of stainless steel. When the collimator 170 is kept at a high temperature, it will be distorted and become curved, as illustrated in FIG. 4. Thus, the surface of the collimator 170 cannot remain parallel to the surface of the target 150 and the collimator 170 will not stop the target atoms with a large-angle sputtering That is, a sputtering processing using a distorted collimator does not have good step-coverage ability. If the collimator 170 distorts excessively, the supporters 165 cannot support it and the collimator falls to the silicon wafer 160, as shown in FIG. 5.
Replacing the distorted collimator with a new apparatus could solve the above problem as mentioned in FIGS. 4 and 5. However, production line supervisors find it difficult to locate distorted collimator until the products on the silicon wafer have low yields or the collimator falls to the silicon wafer, resulting in production line loss in a factory. Therefore, an apparatus for detecting the distortion of the collimator or the variation of the position of the collimator is required for improving the sputter processing equipment.